Many of the white/gray quartzites aren't really quartzite. They are hard like quartzite, but porous like marble, so they need to be sealed regularly.

Will they put it in writing that this slab will not etch, stain or scratch?

You can still do some basic test yourself on a corner of the slab. Bring a glass tile to see if you can scratch the slab and bring a cut lemon to see if it etches the slab. If they won't let you do these basic tests or give you a written guarantee ... that should give you your answer!

@chispa thanks for your response! when asking more questions of the stone company they say:

Yes! We test all our Quartzites just to confirm that they are true Quartzites. Chrome Quartzite is so you don’t have to worry about etch or staining. Any Quartzites that aren’t are classified as Dolomite at PMI. We still recommend sealing Quartzite at least once a year or having it professionally sealed to protect it. I can recommend you to a sealing company if you’d like.

they are super highly recommended/rated in my area as well as my fabricator so hopefully with a good seal it should be pretty durable

A true quartzite shouldn't need to be sealed. I think my Taj Mahal was sealed when it was installed and has never been sealed again in 2.5 years. I also have Taj Mahal outside on my outdoor kitchen and behind my bbq grill and those slabs aren't sealed. Behind the bbq gets covered in smoke and grease, but I'm lazy to climb up there, so only give it a good cleaning every few months. The soot and grease have all come out so far.

As long as you got that statement in writing from the company, then that should help you if anything happens when you start to use the kitchen.

As soon as your fabricator takes possession of the slabs, have him chip off a corner piece and then do some tests at home. Worst case you can fight the slab yard before you cut and install the slabs!